linux-kernel - [PATCH V9 01/15] asm-generic: ticket-lock: Remove unnecessary atomic

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Date:   Mon,  8 Aug 2022 03:13:04 -0400
From:   guoren@...nel.org
To:     palmer@...osinc.com, heiko@...ech.de, hch@...radead.org,
        arnd@...db.de, peterz@...radead.org, will@...nel.org,
        boqun.feng@...il.com, longman@...hat.com, shorne@...il.com,
        conor.dooley@...rochip.com
Cc:     linux-csky@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Guo Ren <guoren@...ux.alibaba.com>, Guo Ren <guoren@...nel.org>
Subject: [PATCH V9 01/15] asm-generic: ticket-lock: Remove unnecessary atomic_read

From: Guo Ren <guoren@...ux.alibaba.com>

Remove unnecessary atomic_read in arch_spin_value_unlocked(lock),
because the value has been in lock. This patch could prevent
arch_spin_value_unlocked contend spin_lock data again.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
---
 include/asm-generic/spinlock.h | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h
index fdfebcb050f4..90803a826ba0 100644
--- a/include/asm-generic/spinlock.h
+++ b/include/asm-generic/spinlock.h
@@ -68,11 +68,18 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 	smp_store_release(ptr, (u16)val + 1);
 }
 
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+	u32 val = lock.counter;
+
+	return ((val >> 16) == (val & 0xffff));
+}
+
 static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
 {
-	u32 val = atomic_read(lock);
+	arch_spinlock_t val = READ_ONCE(*lock);
 
-	return ((val >> 16) != (val & 0xffff));
+	return !arch_spin_value_unlocked(val);
 }
 
 static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
@@ -82,11 +89,6 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
 	return (s16)((val >> 16) - (val & 0xffff)) > 1;
 }
 
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
-	return !arch_spin_is_locked(&lock);
-}
-
 #include <asm/qrwlock.h>
 
 #endif /* __ASM_GENERIC_SPINLOCK_H */
-- 
2.36.1